The Seldinger method is a method of percutaneously introducing a catheter into the inside of a living body, such as into a blood vessel. In the Seldinger method, a hole which communicates the outside with the inside of a living body is formed by puncturing the skin with a needle. Then, a dilator, which has been inserted through the inside of a tubular introducer sheath through which a catheter can be inserted, is inserted into the hole.
The dilator protrudes from a distal end of the introducer sheath, and expands the diameter of the hole with a taper-shaped outer peripheral surface while passing through the hole. Accordingly, an operator senses resistance at the time of inserting the introducer sheath and the dilator into the hole. Here, a proposal is made to decrease the resistance.
In JP-A-2008-11867, for example, to realize decrease of the resistance, puncture resistance at the time when a distal endmost portion of the dilator punctures the hole, and diameter expansion resistance at the time when the dilator passes through the hole and expands the diameter thereof, as the resistances sensed by the operator, are set to be separately applied, rather than being applied substantially at the same time as is generally the case.